Thermal relay



Jan, 13. 1925. 1,522,786

y J. B. MaCNEILL THERMAL RELAY Filed June 9, 1920 ATTORNEY Patented Jan. 1.3, 1925.

UNITI-:D STATES .TOI-IN B..MJLCNEILL, OF WILKINSBURG, PENNSYLVANIA, ASSIGNO TO WESTINGHOUSE ELECTRIC & MANUFACTURING COMPANY, A CORPORATION OF PENNSYLVANIA.

THERMAL RELAY.

Application led .Tune 9, 1920. Serial No. 387,570.

To all whom it may concern:

Be it known that I, JOHN B. MACNEILL, a subject of the King of Great Britain, and a resident of liVilkinsburg, in the county of Allegheny and State of Pennsylvania, have invented a new and useful Improvement in Thermal Relays` of which the following is a specification.

Wy invention relates to electrical protective devices and particularly to thermal relays.

One object of my invention is to provide a thermal relay that shall have a sufficient time interval in the operation thereof to effect protection of electrical apparatus against overloads.

Another object of my invention is to provide a thermal relay, of the above-indicated character, that shall not require the use of a separate heat-storage member.

A further object of my invention is to provide a helical spring that shalll have sufficient heat-storage capacity and torque to constitute a thermal relay of the above-indicated character.

A further object of my invention is to provide means for effecting quick operation ot' the relay.

A further object of my invention is to provide a relay. of the above-indicated character. that shall be adapted to be used in ordinary cartridge-fuse clips, and be reliable and eifective in its operation.

llcretofore, thermal relays having such characteristics that they conform to the heating characteristics of the device to be protected have been constructed without the use of a heating winding. However, these were for protective devices of large currentcarrying capacity because it was diicult to obtain sutlicient torque in the relay and, at the same time. Suiiicient heat storage for protecting devices of low current-carrying capacity without the use of auxiliary heating means.

In view of the above, I provide a relay comprising a helical spring that is of such high resistance and of such mechanical strength that sufficient heat-storage is obtained with the required operating torque. The spring is adapted to expand to open a contact member when an overload obtains for a predetermined time on the device to be protected. In other words. the spring has a heating characteristic vcorresponding to the device to be protected, and no auxiliary heating coil or heat-storage member needbe employed. In order to prevent arcing at the contact when it is actuated by the spring, I provide a biased leaf spring that is actuated by the helical spring to control the movement of the contact member.

The single figure of the accompanying drawing is a sectional and diagrammatic view of an electric circuit and device embodying my invention. l

A motor 1 is connected to an electric circuit 2 and is provided with a circuit interi rupter 3 that is controlled by a thermal relay 4 for the purpose of disconnecting the motor 1 from the circuit 2, under predetermined conditions.

The relay 4 comprises a casing 5 constructed of insulating material and Vhaving connecting ferrules 6 and'7 1at the ends thereof to be received by standard fuse clips, if desired. A biased lea-f spring 8 is disposed in the casing 5 near one end thereof and is maintained in its biased position by means of a bent spring 9 that is secured at one end 11 thereof to the ferrule 7 by means of a screw 10. A contact-supporting member 12 is mounted on the biased leaf spring 8 and comprises a laterally disposed arm 13 and a longitudinally disposed arm 14. A contact member 15 is secured to the arm 14 and is adapted to engage a stationary contact member 16 that is connected to one terminal of a holding coil 17 of the interrupter 3, the other terminal of which is connected to the conductor 18 of the circuit 2. A helical spring 19 is connected to the ferrule 6 and is disposed between the ferrule 6 and the leaf spring S, thus occul pying` substantially the total length ofthe relay casing and being of such resistance as to constitute al heat-storage member which. when sufficient heat is stored therein` will expand to cause the spring 8 to disengage the Contact members 15 and 16 through the arms 13 and 14.

Since the resistance of lthe spring 19 is Vrelatively largez the spring may be of sufresponding to the heating characteristic of in fuse-type clips, comprisinga tubular 50 i the lmotor 1, for ordinary protective purmember provided with endferrules, a biased poses, it is only necessary that a suiiicient leaf spring disposed within the tubular time interval be obtained in the device to member adjacent one end thereof, means for ensure that thercircuit interrupter 3 will be electrically connecting the leaf spring to the opened by its spring 2() before the temperadjacent ferrule, a helical spring disposed 5 ature of the motor 1 reaches a destructive between lthe leaf spring and the opposite value. -ferrule, and a movable contact-supporting When sufficient current has traversed the member controlled by the leaf spring. spring 19. which would destroy the motor 4. A thermal relay adapted for insertion 1 if permitted to continue for longer than in fuse-type clips, comprising a tubular 60 a predetermined interval of time, the spring member provided with end ferrules, a biased 19 will expand to open the circuit through leaf spring disposed Within the tubular the Winding 17 and thus permit the spring member adjacent one end lthereof, means 20 to open the c'rcuit through the inter-` for electrically connecting the leaf spring to rupter 3. When the motor l and, consethe adjacent ferrule, a helical spring dis- 65 quently, the spring I19 have cooled to a posed between the leaf spring andthe oppredetermined degree, the contact members posite ferrule, and a contact member con- 15 and 16 will be again closed and the cirtrolled-by the leaf spring.

cuit interrupter 3 may be reclosed to there- 5. A thermal relay adapted for insertion by connect the motor 1 to the circuit 2. By in fuse-type clips, comprising a tubular 70 employing the biased leaf spring 8, quick member provided with end ferrules, a leaf isengagement of the contact members 15 spring disposed within the tubular member and 16 is obtained and dangerous arcing at adjacent one end thereof, means normally the contact surfaces thereof is precluded. biasing the spring in one direction, a ther- My invention is not limited to the specific mally-responsive ,element connected between 75 structure illustrated, as it may be variously the ferrules and operative to bias the spring modified without departing from the spirit in another direction and a contact member and scope thereof, as set forth in the apcontrolled by the spring.

pended claims. t 6. A thermal relay comprising a cylin- I claim as my invention: drical casing, a movable contact member 80 1. A protective device for opening an electherein, a thermal-responsive member for tric circuit containing electric apparatus actuating the contact member and means upon a predetermined temperature rise simultaneously actuated by the thermalabove a predetermined value in said circuit responsive member for causing the actuation comprising a helical spring connected in of the contact member to be efected with a Se circuit with said apparatus and adapted-to snap action. have a heating characteristic corresponding 7. A thermal relay comprising a cartridge to the heating characteristic of the appacas1ng.an expansible spring disposed thereratus, a contact member and means actuated in, a biad leaf spring controlled by the bythe spi'ing for controlling the contact expaiisible spring and a contact member 90, member. mounted on, and controlled by, the biased 2. A thermal relay foi' an electric circuit spring to actuate said contact member with containing electric apparatus comprising a a snap action. helical spring in circuit with the apparatus, In testimony whereof, I have hereunto a' biased leaf spring controlled thereby and subscribed my name this 3rd day of June, 95

a contact member controlled bythe leaf 1920.

spring to effect quick movement thereof.

3. vA thermal relay adapted for insertion J OHN B., MAcNEILL. 

